The present invention is directed toward magnetic recording heads and, more particularly, toward magnetic recording heads designed to minimize write asymmetry.
The ability to increase the storage capacity in magnetic recording is an ongoing concern. As the amount of information to be stored continues to increase, demands for high density recording also continue to increase. In conventional longitudinal magnetic recording systems, as areal densities approach 100 Gbit/in2 it has become increasingly difficult to meet the requirements of thermal stability (the degradation of written information due to thermal fluctuations), SNR(Signal-To-Noise Ratio) and writeability. Improving on one of the requirements typically results in a tradeoff negatively effecting another requirement. For example, while the SNR can be increased by reducing the grain size of the recording medium, which is normally 200 xc3x85 thick, reducing the grain size of the media results in a decrease in thermal stability. While the thermal stability can be increased by increasing the anisotropy of the recording medium, e.g., using a different alloy, this results in a decrease in writeability. While reducing the Bit Aspect Ratio (BAR) has been proposed to extend longitudinal recording up to 100 Gbit/in2, the above-identified problems remain as fundamental limitations inherent in conventional longitudinal magnetic recording systems.
As the longitudinal magnetic recording technology reaches its limit in areal density due to thermal stability, SNR and writeability requirements, perpendicular magnetic recording systems (in which the recording medium is magnetized in a direction perpendicular to the plane of the recording medium) have been proposed to possess the potential for higher recording densities. Various modeling and simulations have suggested that perpendicular recording is superior to conventional longitudinal recording due to various reasons, including, but not limited to, larger optimal medium thickness, better write field efficiency, and less demagnetizing fields from the stored bit patterns. Perpendicular recording, coupled with the use of a soft under-layer media, is considered a strong candidate to extend recording densities by achieving sharp transitions, even with the use of a thicker magnetic recording layer. With the soft under-layer media, stronger recording fields can be generated, which in turn allow the use of higher anisotropy media. The higher anisotropy media, coupled with the thicker magnetic recording layer, is projected to provide a gain of a factor of 5-10 in recording densities for the same thermal stability criterion.
FIG. 2 illustrates a typical example of a conventional perpendicular magnetic recording head, shown generally at 10. The magnetic recording head 10 has a single (main pole) pole for generating field at the media 11, and is conventionally known as a single pole magnetic head. The magnetic recording head 10 includes a main pole 12, a return pole 14 and a magnetic via 15 connecting the main 12 and return 14 poles. An electrically conductive magnetizing coil 16 surrounds the magnetic via 15. The recording media 11 typically includes a substrate 18, a soft magnetic underlayer 20 formed on the substrate 18, and a perpendicularly magnetized recording layer 22 formed on the soft underlayer 20.
When writing, the magnetic recording head 10 is separated from the recording media 11 by a distance known as the xe2x80x9cfly heightxe2x80x9d. The recording media 11 is moved past the magnetic recording head 10 so that the recording head 10 follows the tracks of the recording media 11. The coil 16 is transversed by a current and produces a magnetic flux 24 channeled by the main pole 12 to produce an intense writing flux at the tip 26 of the main pole 12 which records the information in the magnetic recording layer 22. The flux 24 passes from the tip 26 of the main pole 12, through the magnetic recording layer 22, into the soft underlayer 20, and across to the return pole 14, which provides a return path for the flux, thereby forming a closed magnetic circuit in which the magnetic flux in the recording layer 22 directly under the poles of the magnetic recording head 10 is oriented perpendicular to the plane of the recording layer 22. The cross-sectional area of the return pole 14 is larger than that of the main pole 12 to ensure that the flux density at the return pole 14 is sufficiently reduced as not to magnetize the recording layer 22.
While perpendicular recording has its advantages over longitudinal recording, the use of the soft underlayer 20 poses some challenges during writing as well as reading. Because of the relatively high permeability of the soft underlayer, transitions previously recorded on adjacent tracks can influence the transitions being written at the main pole 12. Depending on the magnetization state of the tracks adjacent to the written track, an asymmetry is introduced in the written di-bit response. This is typically referred to as the xe2x80x9cneighborhood effectxe2x80x9d.
FIG. 1 shows two written di-bits, at 26 and 28, separated by an isolated transition, at 30, using a conventional single pole perpendicular recording head on a recording media with a soft underlayer. Three different states of magnetization of the neighboring track are illustrated in FIG. 1, namely, AC erase (neighboring track not magnetized), DC erase (+) (neighboring track magnetized upward) and DC erase (xe2x88x92) (neighboring track magnetized downward). As shown in FIG. 1, depending on the magnetization state of the neighboring track, i.e, DC erase (+) or DC erase (xe2x88x92), an asymmetry is seen in the corresponding di-bit pattern. This asymmetry is illustrated in both a change in amplitude of the measured flux and a time shift in the written di-bit pattern. The time shift asymmetry in the di-bit pattern and the amplitude asymmetry in the amplitude of the di-bits shows as a measurable time shift for an isolated transition. Since the magnetization pattern from the neighboring tracks changes depending on the data stored on the neighboring tracks, this will change the di-bit asymmetry. This asymmetry will effect the performance of linear channels and degrade the areal density that can be achieved by those linear channels. Further, the effects of the di-bit pattern asymmetry become even more evident at smaller track widths, i.e., higher areal densities.
Additionally, stray magnetic fields from the other components in the disc drive also can corrupt the recorded information. These stray magnetic fields couple with the main pole 12 of the recording head 10 and either add to or subtract from the write field, producing further written asymmetry and transition shifts.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
A single pole magnetic recording head is provided according to the present invention for perpendicular magnetic recording on a recording medium. The magnetic recording head includes a main magnetic pole having a first end positionable adjacent the recording medium and a second end spaced from the first end. A coil is magnetically coupled to the main magnetic pole for producing a write flux. The magnetic recording head further includes a magnetic return pole forming first and second return paths for the magnetic flux. The magnetic return pole includes first and second return poles disposed on opposite sides of, and spaced from, the main magnetic pole, and a magnetic via connecting the first and second return poles and extending over the main magnetic pole forming a back shield. The main magnetic pole is isolated from the magnetic return pole by a control gap of non-magnetic material between the second end of the main magnetic pole and the magnetic via to effectively isolate the main magnetic pole from the magnetic return pole.
In one form, the magnetic return pole is formed of a magnetic material having a first saturation magnetization and anisotropy, with the main magnetic pole formed of a magnetic material having a second saturation magnetization and anisotropy which may be greater than the first saturation magnetization and anisotropy.
In another form, the coil surrounds the main magnetic pole. The first and second return poles include first and second ends, respectively, positionable adjacent to the recording medium. The first and second return poles may include first and second front shields, respectively, adjacent the first and second ends, respectively. The first and second front shields are made of the same material as the magnetic return pole and extend toward the main magnetic pole such that the first and second front shields are disposed between the coil and the recording medium.
In yet another form, the coil includes first and second coils surrounding the magnetic via on opposite sides of the main magnetic pole.
In still another form, the magnetic return pole includes first and second symmetrical magnetic return poles forming symmetrical magnetic return paths for the magnetic flux. The symmetrical first and second return poles are positioned one upstream and one downstream of the main magnetic pole relative to the direction of movement of the recording medium.
In a further form, the main magnetic pole first end and the first and second ends of the first and second return poles lie in the same plane, such that with the magnetic recording head utilized for perpendicular magnetic recording the first end of the main magnetic pole and the first and second ends of the first and second return poles, respectively, are the same distance from the recording medium.
The field under the first and second return poles must be small as to not corrupt neighboring tracks and, therefore, the cross-sectional areas of the first and second return poles must be larger than the cross-sectional area of the main magnetic pole.
A magnetic recording head is also provided according to an additional embodiment of the present invention for magnetic recording on recording medium. The magnetic recording head includes a main magnetic pole having a first end positionable adjacent to the recording medium and a second end spaced from the first end. A coil is provided which is magnetically coupled to the main magnetic pole to produce a write flux. The magnetic recording head includes a magnetic return pole forming first and second return paths for the magnetic flux. The magnetic return pole includes first and second return poles disposed on opposite side of, and spaced from, the main magnetic pole, and a back shield connecting the first and second return poles. The back shield includes first and second magnetic vias extending from the first and second return poles, respectively, and a non-magnetic portion connecting the first and second magnetic vias. The second end of the main magnetic pole is disposed in the non-magnetic portion, such that the nonmagnetic portion surrounds the second end of the main magnetic pole. The main magnetic pole is separated from the magnetic return pole by a control gap of the non-magnetic portion material between the second end of the main magnetic pole and the first and second magnetic vias to effectively isolate the main magnetic pole from the magnetic return pole.
It is an aspect of the present invention to minimize write asymmetry in perpendicular magnetic recording.
It is further aspect of the present invention to reduce the effects of external stray magnetic fields in perpendicular magnetic recording.
Other aspects and advantages of the present invention can be obtained from the study of the specification, the drawings, and the appended claims.